Subsea wellbore drilling system for reducing bottom hole pressure

Abstract

The present invention provides drilling systems for drilling subsea wellbores. The drilling system includes a tubing that passes through a sea bottom wellhead and carries a drill bit. A drilling fluid system continuously supplies drilling fluid into the tubing, which discharges at the drill bit bottom and returns to the wellhead through an annulus between the tubing and the wellbore carrying the drill cuttings. A fluid return line extending from the wellhead equipment to the drilling vessel transports the returning fluid to the surface. In a riserless arrangement, the return fluid line is separate and spaced apart from the tubing. In a system using a riser, the return fluid line may be the riser or a separate line carried by the riser. The tubing may be coiled tubing with a drilling motor in the bottom hole assembly driving the drill bit. A suction pump coupled to the annulus is used to control the bottom hole pressure during drilling operations, making it possible to use heavier drilling muds and drill to greater depths than would be possible without the suction pump. An optional delivery system continuously injects a flowable material, whose fluid density is less than the density of the drilling fluid, into the returning fluid at one or more suitable locations the rate of such lighter material can be controlled to provide supplementary regulation of the pressure. Various pressure, temperature, flow rate and kick sensors included in the drilling system provide signals to a controller that controls the suction pump, the surface mud pump, a number of flow control devices, and the optional delivery system.

What is claimed is:  
     
       1. A method of controlling bottomhole pressure during drilling of a wellbore with a drill string having a bottomhole assembly at an end of a tubing and wherein a drilling fluid supplied under pressure during drilling to the tubing returns to the surface (“the return fluid”), said method comprising: 
       (a) providing a pump in the return fluid;  
       (b) determining a parameter relating to the drilling fluid; and  
       (c) controlling the speed of the pump in the return fluid in response to the determined parameter to control the bottomhole pressure.  
     
     
       2. The method of  claim 1 , wherein the parameter is pressure of the drilling fluid at a selected location. 
     
     
       3. The method of  claim 2 , wherein the selected location is one of (i) at a wellhead placed over the wellbore; (ii) adjacent an inlet of the pump; (iii) adjacent bottom of the wellbore; and (iv) in an annulus between the wellbore and surrounding formation; (v) at the surface; (vi) in the bottomhole assembly; (vii) in the drill string; (viii) in a return line associated with the return fluid; and (ix) in a riser between a wellhead on the wellbore and the surface. 
     
     
       4. The method of  claim 2 , wherein the desired pressure is above the pore pressure of a formation surrounding the wellbore. 
     
     
       5. The method of  claim 2 , wherein the desired pressure is below the fracture pressure of a formation surrounding the wellbore. 
     
     
       6. The method of  claim 2 , wherein the desired pressure is within a predetermined range of pressures. 
     
     
       7. The method of  claim 1 , wherein the parameter relating to the drilling fluid is a flow rate of the drilling fluid. 
     
     
       8. The method of  claim 1  further comprising providing a control unit to control the pump. 
     
     
       9. The method of  claim 8 , wherein the control unit includes a microprocessor that controls the speed of the pump in response to the determined parameter. 
     
     
       10. The method of  claim 8 , wherein the controller controls the pump in response to the determined parameter in real-time. 
     
     
       11. The method of  claim 1  further comprising: (i) providing a pump at the surface for supplying drilling fluid under pressure; and (ii) controlling the surface pump in conjunction with the pump in the return fluid to control the bottomhole pressure. 
     
     
       12. The method of  claim 1 , wherein providing the pump includes coupling the pump to an annulus of the wellbore. 
     
     
       13. A wellbore system for controlling bottomhole pressure comprising: 
       (a) a drill string having a bottomhole assembly at an end thereof in the wellbore;  
       (b) a fluid system supplying fluid under pressure to a fluid circulation system, said fluid returning via a return path carrying cuttings (“the return fluid”);  
       (c) a sensor for measuring a selected parameter of the fluid;  
       (d) a pump associated with the return fluid; and  
       (e) a controller controlling the speed of the pump in response to the selected parameter to control the bottomhole pressure at a desired value.  
     
     
       14. The wellbore system of  claim 13 , wherein the selected parameter is pressure. 
     
     
       15. The wellbore system of  claim 14 , wherein the pressure is measured at one of (i) a wellhead placed over the wellbore; (ii) adjacent an inlet of the pump; (iii) adjacent bottom of the wellbore; (iv) in an annulus between the wellbore and surrounding formation; (v) at the surface; (vi) in the bottomhole assembly; (vii) in the drill string; (viii) in a return line associated with the return fluid; and (ix) in a riser between a wellhead over the wellbore and the surface. 
     
     
       16. The wellbore system of  claim 13 , wherein the desired pressure is above pore pressure of formation surrounding the wellbore. 
     
     
       17. The wellbore system of  claim 13 , wherein the desired pressure is below the fracture pressure of formation surrounding the wellbore. 
     
     
       18. The wellbore system of  claim 13 , wherein the desired pressure is within a predetermined range. 
     
     
       19. The wellbore system of  claim 13 , wherein the controller is at one of (i) in the drill string; (ii) bottomhole assembly; and (iii) at the surface. 
     
     
       20. The wellbore system of  claim 13  further comprising a surface pump that supplies fluid under pressure and wherein the controller controls the surface pump in conjunction with the pump in the return fluid to control the bottomhole pressure. 
     
     
       21. The wellbore system of  claim 13 , wherein the pump is in the wellbore. 
     
     
       22. The wellbore system of  claim 13 , wherein the pump is in an annulus of the wellbore. 
     
     
       23. The wellbore system of  claim 13 , wherein the control of the pump overcomes at least a portion of the hydrostatic pressure and friction less pressure of the return fluid. 
     
     
       24. A method of controlling bottomhole pressure during drilling of a wellbore with a drill string having a bottomhole assembly at an end of a tubing and wherein a drilling fluid supplied under pressure during drilling to the tubing returns to the surface (“the return fluid”), said method comprising: 
       (a) providing a pump in the wellbore for pumping the return fluid toward surface and to control the bottomhole pressure at a desired pressure during drilling of the wellbore;  
       (b) determining bottomhole pressure during drilling of the wellbore;  
       (c) controlling the pump in response to the determined bottomhole pressure to control the bottomhole pressure at the desired pressure.  
     
     
       25. The method of  claim 24 , wherein providing the pump in the wellbore comprises coupling the pump to an annulus of the wellbore. 
     
     
       26. The method of  claim 24 , wherein the desired pressure is within a predetermined range of pressure. 
     
     
       27. The method of  claim 24 , wherein controlling the pump includes controlling the speed of the pump to control the bottomhole pressure and thereby equivalent circulating density at the wellbore bottom. 
     
     
       28. A method of controlling pressure in a wellbore during drilling of the wellbore with a drill string having a bottomhole assembly at an end of a drill string and wherein a drilling fluid supplied to a circulation system returns via a return path (“the return fluid”), the method comprising: 
       (a) providing a pump in the wellbore;  
       (b) determining a parameter of interest; and  
       (c) controlling the pump in response to the determined parameter to control the bottomhole pressure.  
     
     
       29. The method of  claim 28 , wherein the determined parameter is pressure. 
     
     
       30. The method of  claim 29 , wherein the pressure is determined at a location selected from one of (i) at a wellhead placed over the wellbore; (ii) adjacent an inlet of the pump; (iii) adjacent bottom of the wellbore; and (iv) in an annulus between the wellbore and surrounding formation; (v) at the surface; (vi) in the bottomhole assembly; (vii) in the drill string; (viii) in a return path; and (ix) in a riser between a wellhead on the wellbore and the surface. 
     
     
       31. The method of  claim 28  wherein the parameter of interest is selected from one of: (i) flow; (ii) relating to the drilling of the wellbore; (iii) relating to the formation that is being drilled; (iv) relating to the drilling fluid; and (v) relating to the bottom hole assembly used for drilling the wellbore. 
     
     
       32. The method of  claim 28 , wherein controlling the pump controls the bottomhole pressure at one of: (i) above the pore pressure of a formation surrounding the wellbore; (ii) below the fracture pressure of a formation surrounding the wellbore; (iii) within a predetermined range of pressures; and (iv) at a selected pressure. 
     
     
       33. The method of  claim 28  further comprising providing a controller that controls the pump in response to the determined parameter. 
     
     
       34. The method of  claim 28  further comprising: (i) providing a pump at the surface for supplying drilling fluid under pressure; and (ii) controlling the surface pump in conjunction with the pump in the return fluid to control the bottomhole pressure. 
     
     
       35. The method of  claim 28 , wherein providing the pump includes coupling the pump to an annulus of the wellbore. 
     
     
       36. A wellbore system for controlling bottomhole pressure comprising: 
       (a) a drill string having a bottomhole assembly at an end thereof in a wellbore;  
       (b) a fluid system supplying fluid under pressure to the wellbore, said fluid returning via a return path (“the return fluid”);  
       (c) a pump positioned in the wellbore;  
       (d) a sensor for measuring a selected parameter; and  
       (e) a controller controlling the pump in response to the selected parameter to control the bottomhole pressure.  
     
     
       37. The wellbore system according to  claim 36 , wherein said selected parameter is pressure of the drilling fluid at a location selected from one of (i) at a wellhead placed over the wellbore; (ii) adjacent an inlet of the pump; (iii) adjacent bottom of the wellbore; and (iv) in an annulus between the wellbore and surrounding formation; (v) at the surface; (vi) in the bottomhole assembly; (vii) in the drill string; (viii) in a return line associated with the return fluid; and (ix) in a riser between a wellhead on the wellbore and the surface. 
     
     
       38. The wellbore system according to  claim 36 , wherein said controller controls the pump to maintain the bottomhole pressure at one of: (i) above the pore pressure of a formation surrounding the wellbore; (ii) below the fracture pressure of a formation surrounding the wellbore; (iii) within a predetermined range of pressures; and (iv) at a selected pressure. 
     
     
       39. The wellbore system according to  claim 36 , wherein the selected parameter is selected from one of: (i) flow; (ii) relating to the drilling of the wellbore; (iii) relating to the formation that is being drilled; and (iv) related to the bottom hole assembly used for drilling the wellbore. 
     
     
       40. A method of controlling bottomhole pressure during drilling of a wellbore with a drill string having a bottomhole assembly at an end of a tubing and wherein a drilling fluid supplied to a circulation system returns via a return path (“the return fluid”), the method comprising: 
       (a) providing a pump in the return fluid;  
       (b) operating the pump during drilling of the wellbore;  
       (c) determining a parameter of interest; and  
       (d) controlling the pump during drilling of the wellbore in response to the determined parameter to control the bottomhole pressure.  
     
     
       41. The method of  claim 40 , wherein the determined parameter is pressure. 
     
     
       42. The method of  claim 41 , wherein the pressure is determined at one of (i) at a wellhead placed over the wellbore; (ii) adjacent an inlet of the pump; (iii) adjacent bottom of the wellbore; and (iv) in an annulus between the wellbore and surrounding formation; (v) at the surface; (vi) in the bottomhole assembly; (vii) in the drill string; (viii) in a return line associated with the return fluid; and (ix) in a riser between a wellhead on the wellbore and the surface. 
     
     
       43. The method of  claim 40 , wherein the controlling the pump controls the bottomhole pressure at one of: (i) above the pore pressure of a formation surrounding the wellbore; (ii) below the fracture pressure of a formation surrounding the wellbore; (iii) within a predetermined range of pressures; and (iv) at a selected pressure. 
     
     
       44. The method of  claim 40 , wherein the parameter of interest is selected from one of: (i) flow; (ii) relating to the drilling of the wellbore; (iii) relating to the formation that is being drilled; (iv) relating to the drilling fluid; and (v) relating to the bottom hole assembly used for drilling the wellbore. 
     
     
       45. The method of  claim 40  further comprising providing a controller to control the pump. 
     
     
       46. The method of  claim 45 , wherein the controller controls the pump in response to the determined parameter in real-time. 
     
     
       47. The method of  claim 40  further comprising: (i) providing a pump at the surface for supplying drilling fluid under pressure; and (ii) controlling the surface pump in conjunction with the pump in the return fluid to control the bottomhole pressure. 
     
     
       48. The method of  claim 40 , wherein providing the pump includes coupling the pump to an annulus of the wellbore. 
     
     
       49. A wellbore system for controlling bottomhole pressure comprising: 
       (a) a drill string having a bottomhole assembly at an end thereof in the wellbore;  
       (b) a fluid system supplying fluid under pressure to the wellbore, said fluid returning via a return path carrying cuttings (“the return fluid”);  
       (c) a sensor for measuring a selected parameter of interest;  
       (d) a pump positioned in the return fluid, the pump operating during drilling of the wellbore; and  
       (e) a controller controlling the pumb during drilling of the wellbore in response to the selected parameter to control the bottomhole pressure.  
     
     
       50. The wellbore system according to  claim 49 , wherein said selected parameter is pressure of the drilling fluid at a location selected from one of (i) at a wellhead placed over the wellbore; (ii) adjacent an inlet of the pump; (iii) adjacent bottom of the wellbore; and (iv) in an annulus between the wellbore and surrounding formation; (v) at the surface; (vi) in the bottomhole assembly; (vii) in the drill string; (viii) in a return line associated with the return fluid; and (ix) in a riser between a wellhead on the wellbore and the surface. 
     
     
       51. The wellbore system according to  claim 49 , wherein said controller maintains the bottomhole pressure at one of: (i) above the pore pressure of a formation surrounding the wellbore; (ii) below the fracture pressure of a formation surrounding the wellbore; (iii) within a predetermined range of pressures; and (iv) at a selected pressure. 
     
     
       52. The wellbore system according to  claim 49 , wherein the selected parameter is selected from one of: (i) flow; (ii) relating to the drilling of the wellbore; (iii) relating to the formation that is being drilled; (iv) relating to the drilling fluid; and (v) relating to the bottom hole assembly used for drilling the wellbore. 
     
     
       53. The wellbore system according to  claim 49 , wherein said controller controls said pump in response to said selected determined parameter in real-time. 
     
     
       54. The wellbore system according to  claim 49  further comprising: a pump at the surface for supplying drilling fluid under pressure, said surface pump configured to be controlled in conjunction with the pump in the return fluid to control the bottomhole pressure. 
     
     
       55. The wellbore system according to  claim 49 , wherein said pump is coupled to an annulus of the wellbore. 
     
     
       56. A method of controlling bottomhole pressure during drilling of a wellbore with a drill string having a bottomhole assembly at an end of a tubing and wherein a drilling fluid supplied under pressure during drilling to the tubing returns to the surface (“the return fluid”), said method comprising: 
       (a) providing a pump in the return fluid;  
       (b) selecting a desired bottomhole pressure;  
       (c) determining a selected parameter of interest; and  
       (d) controlling the flow rate of the pump in the return fluid in response to the determined parameter to control the bottomhole pressure at the desired pressure.  
     
     
       57. The method of  claim 56 , wherein the selected parameter is pressure. 
     
     
       58. The method of  claim 57 , wherein the pressure is determined at one of (i) at a wellhead placed over the wellbore; (ii) adjacent an inlet of the pump; (iii) adjacent bottom of the wellbore; and (iv) in an annulus between the wellbore and surrounding formation; (v) at the surface; (vi) in the bottomhole assembly; (vii) in the drill string; (viii) in a return line associated with the return fluid; and (ix) in a riser between a wellhead on the wellbore and the surface. 
     
     
       59. The method of  claim 56 , wherein the controlling the pump provides a bottomhole pressure at one of: (i) above the pore pressure of a formation surrounding the wellbore; (ii) below the fracture pressure of a formation surrounding the wellbore; (iii) within a predetermined range of pressures; and (iv) at a selected pressure. 
     
     
       60. The method of  claim 56 , wherein the selected parameter is selected from one of: (i) flow; (ii) relating to the drilling of the wellbore; (iii) relating to the formation that is being drilled; (iv) relating to the drilling fluid; and (v) relating to the bottom hole assembly used for drilling the wellbore. 
     
     
       61. The method of  claim 56  further comprising providing a controller to control the pump. 
     
     
       62. The method of  claim 56 , wherein the controller controls the pump in response to the determined parameter in real-time. 
     
     
       63. The method of  claim 56  further comprising: (i) providing a pump at the surface for supplying drilling fluid under pressure; and (ii) controlling the surface pump in conjunction with the pump in the return fluid to control the bottomhole pressure. 
     
     
       64. The method of  claim 56 , wherein providing the pump includes coupling the pump to an annulus of the wellbore. 
     
     
       65. A wellbore system for controlling bottomhole pressure comprising: 
       (a) a drill string having a bottomhole assembly at an end thereof in the wellbore;  
       (b) a fluid system supplying fluid under pressure to the tubing, said fluid returning to the surface carrying cuttings (“the return fluid”);  
       (c) a sensor for measuring a selected parameter of interest;  
       (d) a pump associated with the return fluid; and  
       (e) a controller controlling the flow rate of the pump in response to the selected parameter to control the bottomhole pressure at a desired value.  
     
     
       66. The wellbore system according to  claim 65 , wherein said selected parameter is pressure of the drilling fluid at a location selected from one of (i) at a wellhead placed over the wellbore; (ii) adjacent an inlet of the pump; (iii) adjacent bottom of the wellbore; and (iv) in an annulus between the wellbore and surrounding formation; (v) at the surface; (vi) in the bottomhole assembly; (vii) in the drill string; (viii) in a return line associated with the return fluid; and (ix) in a riser between a wellhead on the wellbore and the surface. 
     
     
       67. The wellbore system according to  claim 65 , wherein said controller maintains the bottomhole pressure at one of: (i) above the pore pressure of a formation surrounding the wellbore; (ii) below the fracture pressure of a formation surrounding the wellbore; (iii) within a predetermined range of pressures; and (iv) at a selected pressure. 
     
     
       68. The wellbore system according to  claim 65 , wherein the selected parameter is selected from one of: (i) flow; (ii) relating to the drilling of the wellbore; (iii) relating to the formation that is being drilled; (iv) relating to the drilling fluid; and (v) relating to the bottom hole assembly used for drilling the wellbore. 
     
     
       69. The wellbore system according to  claim 65 , wherein said controller includes a microprocessor that controls the speed of said pump in response to the selected parameter. 
     
     
       70. The wellbore system according to  claim 65 , wherein said controller controls said pump in response to said selected determined parameter in real-time. 
     
     
       71. The wellbore system according to  claim 65  further comprising: (i) a pump at the surface for supplying drilling fluid under pressure, said surface pump configured to be controlled in conjunction with the pump in the return fluid to control the bottomhole pressure. 
     
     
       72. The wellbore system according to  claim 65 , wherein said pump is coupled to an annulus of the wellbore.